经脉，络脉

Is there any evidence that the terms 经脉 and 络脉 were used to describe veins and arteries?

According to the textbook I'm reading now*, both arteries and veins are organized by size into 经脉，络脉和孙络 (from big to small), and, although the to-and-away-from-the-heart aspect of the blood vessel system is part of TCM physiology (since when???), the terms 经脉 and 络脉 are not equivalent to artery and vein.

The character 脉 was originally used for a place where the pulse could be felt, so why would a large vein be called X脉? I don't get it...

*the official preparation text for the Chinese TCM doctors license...slogging through all 1200 pages of it...